The present invention relates to a die for use in fine press working which is applied to ultra-precision processing of IC lead frames.
As shown in FIG. 6, an IC is generally structured in such a manner that: an IC chip 3 is adhered onto a pad 2 provided in the center of a lead frame 1; tips of inner leads 5 of leads 4 are connected with electrodes of the IC chip 3, using fine wires made of gold, aluminum or copper; and after that, the IC chip 3 is enclosed with mold resin 7. Numeral 5A is an outer lead.
As the IC chip 3 is highly improved, the number of its electrodes is increased. Accordingly, the number of the leads 4 of the lead frame 1 must be increased. However, the more the number of the leads 4 is increased, the smaller the widths of the leads 4 become, and also the more the number of the leads 4 is increased, the smaller the intervals of the leads 4 become, so that it is difficult to punch the leads 4.
FIGS. 7 and 8 show a conventional example of punching. A plate 8 made of copper alloy is successively fed, and the pad 2 is formed first. Next, as shown in the first process represented by character A, punch holes 9 are formed on both sides of the pad 2. The punch holes 9 are formed with a male die composed by combining and fixing with a holder (not shown) base portions 10B of various punches 10, the tips of which are formed into cutting blades 10A as shown in FIG. 7, a so as to form the male die. Thereafter, new punch holes 9A are formed between the punch holes 9 as shown in the second process represented by character B, and further increasing the number of the punch holes 9 as shown in the processes of C to E. Each of the aforementioned processes is effected by a male and a female die corresponding to each process.
In the aforementioned prior art, for example, all the punch holes 9 on one side of the pad 2 can not be punched simultaneously. Therefore, they are punched through a plurality of processes. Accordingly, there is a risk of lowering the efficiency of the punching operation.
In order to solve the aforementioned problem, a means is suggested in which a large number of punches are provided to the male die correspondingly to punch holes. However, when the male die provided with a large number of punches is used to punch a plate continuously, there is a possibility that the narrow punches are deformed and damaged. The reason is that the punches being held by the holder through their base portions 10B, the strength of the punch 10 at the time of punching is low. Especially because the thickness of the punch 10 on the cutting blade 10A side is extremely thin.